1. Field of the Invention
The present invention relates to a semiconductor device fabricating method and a semiconductor device fabricating system. More specifically, the present invention relates to a semiconductor device fabricating method that forms a tungsten nitride film (WNx film) for using as wiring lines, a barrier-metal or electrodes, and a system for carrying out the same.
2. Description of the Related Art
The resistance of gates of semiconductor devices, such as field-effect transistors, increases with the miniaturization of the semiconductor devices. Therefore, desired is materials for forming wiring lines and electrodes, capable of forming a gate having a low resistance even if the gate is miniaturized. Known conductive polysilicon films (poly-Si films) have been replaced in recent years with metal silicide films having a high melting point, such as tungsten silicide films. Recently, tungsten films have been believed to be promising because tungsten films are capable of forming gates having a resistance lower by one figure than that or gates formed from tungsten silicide films.
A laminated film including a tungsten film for forming electrodes is formed by laminating a gate oxide film, a poly-Si film and a tungsten film. If the tungsten film is laminated directly to the poly-Si film, portions of the poly-Si film and the tungsten film facing the interface between the poly-Si film and the tungsten film interact and produce tungsten silicide (WSi) when the laminated film is subjected to a heat treatment process (850 to 900xc2x0 C.) The tungsten silicide (WS1) produced in the interface increases the resistance of the electrode formed from the laminated film. If active reaction between the poly-Si film and the tungsten film takes place in the interface, the tungsten forming the tungsten film will further diffuse through the gate oxide film into a silicon wafer supporting the laminated film, which may increase leakage current that leaks from the transistor or reduce breakdown voltage.
When using a tungsten film for forming an electrode, it is general to prevent interaction between tungsten and poly-Si by sandwiching a barrier film, i.e., a metal nitride film having a high melting point, such as a tungsten nitride film or titanium nitride film, between the tungsten film and the poly-Si film. The tungsten nitride film is stable at rather high temperatures and can be formed of crystal grains of a crystal structure other than a columnar structure. And also large tungsten crystal grains can be grown on the tungsten nitride film to form a tungsten film having a low resistivity. However, the titanium nitride film can be formed of crystal grains only of a columnar structure, and tungsten film to be formed over this titanium nitride film has only limited grain sizes.
Incidentally, the following are known methods for forming tungsten nitride films, i.e., preferable gate barrier films.
(1) Thermal CVD method using WF6 gas (tungsten hexafluoride gas) and NH3 gas (ammonia gas)
(2) Plasma CVD method using WF6 gas and NH3 gas, such as disclosed in JP-A No. 50515/1989
(3) Plasma CVD method using WF6 gas, N2 gas and H2 gas, such as disclosed in JP-A No. 50515/1989
(4) Plasma CVD method using WF6 gas and NF3 gas (nitrogen trifluoride gas) (Suzuki, et al., xe2x80x9cAdvanced Metalization and Interconnect Systems for ULSI Application in 1997xe2x80x9d, Mter. Res. Soc., 1998, 49)
(5) Thermal CVD method using organic tungsten source (Sun, et al., Proc. of 13th VMIC, 151, 1996)
The thermal CVD method of (5) needs a high film forming temperature exceeding 600xc2x0 C. and the diffused layer of a transistor may possibly be damaged at such a high film forming temperature. The film forming methods of (1) to (4) use film forming temperatures in the range of 450 to 500xc2x0 C. and hence do not encounter any problem like that encountered by the film forming method of (5).
The film forming methods of (2) to (4) using a plasma are easy to give damage to the gate oxide and have poor step coverage of via holes or the like, and need an expensive film forming system.
The film forming method of (1) is a thermal CVD method that does not need any plasma and hence does not encounter any problem like that encountered by the plasma CVD methods of (2) to (4). However, the tungsten nitride film formed by the thermal CVD method of (1), as compared with the tungsten nitride film formed by the plasma CVD method, has a relatively high resistivity. There is a further problem that, when a tungsten film is formed over a tungsten nitride film by a thermal CVD method, and the tungsten film and the tungsten nitride film underlying the former are heat-treated at a temperature in the range of 800 to 900xc2x0 C. for 60 s, the tungsten film peels from the tungsten nitride film.
As a result, the thermal CVD method of (1) using WF6 gas and NH3 gas is preferable for the method of forming tungsten nitride films. However, in the method of (1), the tungsten film is liable to peel at the heat-treatment step after forming the tungsten nitride film. And also the tungsten nitride film has a relatively high resistivity.
Sometimes, a tungsten nitride film formed by a prior film forming method contains fluorine in a high content. The fluorine contained in the tungsten nitride film affects adversely the reliability of a semiconductor device fabricated by using the tungsten nitride film. Accordingly, it is desired to determine film forming conditions that should reduce the fluorine content of the film.
In most cases, holes are formed in a surface on which a film is to be deposited. When forming a film on such a surface having holes, the film must be formed over the flat surface and over the bottoms of the holes in a uniform bottom coverage (step coverage). It is desired that bottom coverage (step coverage), i.e., the ratio of the thickness of the film formed on the bottom of a hole to that of the film formed on the flat surface, is 70% or above.
In most cases, various thermal processes follow the film forming process for forming a tungsten nitride film. Strength of adhesion of the tungsten nitride film to the underlying film must be high enough to prevent the peeling of the tungsten nitride film from the underlying film during the thermal processes. When a tungsten nitride film is used as an electrode of a capacitor, (i) there must be low leakage current and (ii) a Schottky barrier must be formed between the tungsten nitride film and an insulating film. When a tungsten nitride film is used as a barrier layer between layers of different materials, the tungsten nitride film must be capable of suppressing the diffusion of those different material.
The present invention has been made to solve those problems and it is therefore an object of the present invention to provide a semiconductor device fabricating method and a semiconductor device fabricating system capable of forming a tungsten nitride film meeting the foregoing requirements.
The film forming method of (1) using WF6 gas and NH3 gas as source gases produces particles of by-products from the source gases.
The present invention has been made to solve this problem and it is therefore an object of the present invention to provide a semiconductor device fabricating method capable of using WF6 gas and NH3 without producing any by-products from WF6 gas and NH3 gas in a film forming chamber or of expelling by-products if by-products are produced, and a semiconductor device fabricating system. It is also an object of the present invention to provide a semiconductor device fabricating method capable of removing by-products produced from WF6 gas and NH3 gas by in-situ cleaning and by keeping the film forming chamber parts to be the proper temperature at which the by-products do not remain.
The inventors of the present invention made studies of the influence of the by-products towards the film quality that are produced when forming tungsten nitride films by using WF6 gas and NH3 gas as source gases, and have found a fact that NH6F and a compound of NH6F and W are deposited on the inner surface of walls defining a film forming chamber, those deposits absorb the source gases to reduce film forming efficiency, and the deposits become the source of particles. The inventors of the present invention made studies of temperature of the deposition of the by-products on parts disposed in the film forming chamber and have found a fact that the deposition of the by-product on specific parts can be prevented when the temperatures of the specific parts are kept in a specific temperature range.
According to a first aspect of the present invention, a semiconductor device fabricating method comprises a preparatory process that brings a first source gas containing tungsten atoms into contact with a workpiece and not bringing a second source gas containing nitrogen atoms into contact with the workpiece; and a film forming process that forms a tungsten nitride film on the workpiece by using the first source gas and the second source gas so as to fabricate a semiconductor. This method prevents the peeling of the tungsten nitride film from a layer underlying the same during heat treatment after film forming.
Preferably, the preparatory process comprises the steps of: adjusting process pressure at which the workpiece is processed to a value in the range of 0.1 to 20 torr; heating the workpiece at a temperature in the range of 300 to 500xc2x0 C.; and adjusting flow rate of the first source gas to a value in the range of 0.5 to 10 sccm or adjusting partial pressure of the first source gas to a pressure in the range of 5xc3x9710xe2x88x924 to 10 torr. Preferably, the film forming process comprises the steps of: adjusting process pressure at which the workpiece is processed to a value in the range of 0.1 to 50 torr; leading the workpiece at a temperature in the range of 300 to 650xc2x0 C.; adjusting flow rate of the first source gas to a value in the range of 0.5 to 100 sccm or adjusting partial pressure of the first source gas to a pressure in the range of 5xc3x97104 to 50 torr; and adjusting flow rate of the second source gas to a value in the range of 20 to 1000 sccm. For example, the first source gas in tungsten hexafluoride gas and the second source gas is ammonia gas.
According to another aspect of the present invention, a semiconductor device fabricating method comprises a preparatory process that brings either of a first source gas containing tungsten atoms and second source gas containing nitrogen atoms into contact with a workpiece and not bringing the other source gas into contact with the workpiece; and a film forming process that forms a tungsten nitride film on the workpiece by using the first and the second source gas so as to fabricate a semiconductor device.
According to another aspect of the present invention, a semiconductor device fabricating method comprises a film forming process for forming a tungsten nitride film on a workpiece by using a first source gas containing tungsten atoms and a second source gas containing nitrogen atoms, wherein a gas containing silicon atoms is additionally used in the film forming process.
According to another aspect of the present invention, a semiconductor device fabricating method comprises a film forming process for forming a tungsten nitride film on a workpiece by using a first source gas containing tungsten atoms and a second source gas containing nitrogen atoms, and a contact process for bringing a gas containing silicon atoms into contact with the formed tungsten nitride film.
These methods are capable of forming a tungsten nitride film satisfactory in adhesion, coverage, electrical characteristics and performance as a barrier.
Preferably, the method further comprises a nitrogen content increasing process for increasing nitrogen content of a surface layer of the tungsten nitride film. In this case, the nitrogen content increasing process is preferably an annealing process in an atmosphere of a gas containing nitrogen atoms. Alternatively, the nitrogen content increasing process is preferably a plasma-processing process using a plasma of a gas containing nitrogen atoms. Preferably, the method further comprises an oxidizing process for oxidizing a surface of the tungsten nitride film. In this case, the oxidizing process is preferably an annealing process in an oxygen gas atmosphere or an atmosphere of a gas containing oxygen.
According to another aspect of the present invention, a semiconductor device fabricating method comprises a workpiece feed process for providing a workpiece in a film forming chamber defined by a film forming vessel; a temperature adjusting process for adjusting temperature of a gas supply mechanism for supplying source gases into the film forming chamber and of portions of the film forming vessel to be exposed to gases to the temperature capable of preventing the deposition of a by-product produced from tungsten hexafluoride gas and ammonia gas on those portions; and a film forming process for forming a tungsten nitride film on the workpiece by supplying tungsten hexafluoride gas and ammonia gas by the gas supply mechanism into the film forming chamber so as to fabricate a semiconductor device.
This method suppresses the production of the by-products by the interaction of WF6 gas and NH3 gas to maintain the interior of the film forming chamber in a normal condition.
The temperature adjusting process preferably adjusts the temperatures of the gas supply mechanism and of the portions of the film forming vessel to be exposed to gases to values in the range of 100 to 300xc2x0 C.
The film forming process is preferably followed by: a posterior temperature adjusting process for adjusting the temperatures of the gas supply mechanism and of the portions of the film forming vessel to be exposed to gases to predetermined temperatures; and a gas supply process for supplying chlorine trifluoride gas into the film forming chamber. In this case, the posterior temperature adjusting process preferably adjusts the temperatures of the gas supply mechanism and of the portions of the film forming vessel to be exposed to gases to temperatures in the range of 80 to 500xc2x0 C.
According to another aspect of the present invention, a semiconductor device fabricating system, for forming a tungsten nitride film on a workpiece, comprises: a film forming vessel defining a film forming chamber in which a workpiece holding device for holding the workpiece is disposed; a first gas supply mechanism provided with a first inlet port and a first outlet port, for supplying a first source gas containing tungsten atoms into the film forming chamber; a second gas supply mechanism provided with a second inlet port and a second outlet port, which are isolated from the first inlet port and the first outlet port of the first gas supply mechanism, for supplying a second source gas containing nitrogen atoms into the film forming chamber; a temperature adjusting mechanism incorporated into the workpiece holding device; an exhautsing mechanism for exhausting gases from the film forming chamber; and a pressure adjusting mechanism for adjusting pressure in the film forming chamber.
The system may further comprises a third gas supply mechanism for supplying chlorine trifluoride gas into the film forming chamber.
According to another aspect of the present invention, a semiconductor device fabricating system, for forming a tungsten nitride film on a workpiece, comprises: a film forming vessel defining a film forming chamber in which a workpiece holding device for holding the workpiece is disposed; a first gas supply mechanism for supplying tungsten hexafluoride gas into the film forming chamber; a second gas supply mechanism for supplying ammonia gas into the film forming chamber; an exhausting mechanism for exhausting gases from the film forming chamber; and a temperature adjusting mechanism for adjusting temperatures of the first gas supply mechanism, the second gas supply mechanism and portions of the film forming vessel to be exposed to gases.
Preferably, the first gas supply mechanism is provided with a first inlet port and a first outlet port, and the second gas supply mechanism is provided with a second inlet port and a second outlet port which are isolated from the first inlet port and the first outlet port.